Method for controlled positioning of a compound layer in a multilayer device

ABSTRACT

A method for controlled positioning of a compound layer such as TiSi 2  or CoSi 2  in a multilayer device such as a semiconductor is disclosed. The compound surface layer is situated adjacent to an intermediate layer comprised of one of the two types of atoms present in the molecules of the adjacent compound surface layer. The intermediate layer is also situated adjacent to a base layer, such as a semiconductor substrate. An epitaxial silicon layer is the suggested intermediate layer where the surface layer is comprised of TiSi 2  or CoSi 2 . By simultaneously heating the multilayer device and using an appropriate etching process for selectively removing the atoms from the surface of the compound surface layer which are common in both the compound and intermediate layer (i.e., silicon) the intermediate layer can be reduced in thickness and/or fully consumed while the structural integrity of the compound surface layer remains essentially unchanged. This results in positioning the surface layer directly adjacent to the base layer, thus allowing for the controlled placement of the compound layer in the multilayer device.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to multilayer film technologyand more specifically to semiconductor technology. Most particularly,the present invention relates to the controlled positioning of acompound layer, such as a silicide layer, in relation to a semiconductorsubstrate, such as silicon. Such layers are typically used infabricating complementary metal-oxide semiconductors (CMOS) transistors.

2.Background of Prior Art

It is well known by those skilled in the art that the electrical contactbetween a compound layer or film, such as a silicide and the siliconsubstrate in a semiconductor device is critical for good conductivity.Therefore, better contact between the compound layer and the substrateis always desired.

Problems with this contact region have been found when the semiconductorsubstrate contains various dopants which are generally added to improvethe conductivity of the substrate. Contact metallurgists have discoveredthat when attempting to create a titanium silicide (TiSi₂) compoundlayer adjacent to and in contact with the semiconductor substrate, thesemiconductor substrate frequently deteriorates because of the requiredhigh temperature annealing process used to convert the titanium silicideto a more conductive crystalline form, such as C-54 titanium silicide.The high temperature anneal often causes the dopants already present inthe semiconductor substrate to redistribute and, further, creates aroughening of the contact region between the doped semiconductor and theadjacent silicide layer. This roughening can cause the device to shortcircuit.

Another difficulty in positioning titanium directly on a siliconsemiconductor substrate is found with the complication in forming auniformly thin titanium silicide layer in close proximity to devicejunctions. Silicide thicknesses of less than 50 nanometers must becarefully positioned very close to the device junctions to preventleakage or shorting. The precise positioning of such a thin layer isoften difficult.

Yet another shortcoming with the known technology occurs because thedoped silicon frequently chosen for the semiconductor substrate layer ismuch less reactive with titanium than undoped silicon making theformation of a titanium silicide layer more difficult with dopedsilicon. Thus, it is more preferable to grow a titanium silicide layeron a layer of pure or lightly doped silicon than directly on the dopedsilicon.

For these reasons, in some devices, a selective silicon epitaxial layeris grown adjacent to the semiconductor doped silicon layer. Since thisepitaxial silicon layer, commonly referred to as epi-silicon, is usuallyundoped or only lightly doped, it reacts better with the titanium toform a titanium silicide compound surface layer. However, after reactingthe titanium with the epi-silicon layer, portions of the epi-siliconlayer usually remain since it is difficult to control the exactthickness of the epi-silicon needed to react with the metal. Because ofits undoped form, the remaining epi-silicon layer generally degrades thedesired contact between the titanium silicide and the underlyingsemiconductor substrate. This contact resistance caused by theepi-silicon layer renders the semiconductor device less conductive.

The present invention provides for a method of removing the intermediateepitaxial silicon layer without destruction or disturbance to the newlyformed compound surface layer. Removal of the epi-silicon layer alsopositions the surface layer immediately adjacent to the siliconsemiconductor substrate, thus further improving the contact region.

The present invention essentially provides for a controlled method toreduce the thickness of the intermediate epitaxial silicon layer byselectively removing atoms which are of the same type as those atomscomprising the epitaxial layer from the surface of the compound silicidelayer while simultaneously heating the multilayer device, such that thediffusion differential between the compound atoms provides for increasedmobility of one of the two atoms relative to the other. Because of thisdiffusion differential, atoms from the intermediate epitaxial siliconlayer replace the selectively removed silicon atoms until all atoms ofthe epitaxial silicon layer have effectively replaced the removed atomsand are incorporated into the compound molecules. The benefit of theinventive method is that the elimination of the intermediate layercauses the positioning of the compound surface layer to change while itsstructure remains essentially unchanged.

Arima, et al., U.S. Pat. No. 4,983,547, teaches the formation of asilicide film from a deposited film which contains a higher thanstoichiometric concentration of silicon (silicon rich). A film ofaluminum or aluminum alloy is deposited on the silicon rich film,followed by heat treatment to precipitate the excess silicon into thealuminum film, leaving a stoichiometric silicide. However, the referencefails to teach how to eliminate one layer while leaving an adjacentlayer effectively or structurally intact.

Gartner, et al., U.S. Pat. No. 4,248,688, discloses the use of ion beametching to selectively remove platinum or palladium in the presence oftheir silicides. The process relies on high sputter etching ratiosbetween the metals and the silicides. However, the reference fails tointroduce any possibility of moving the silicide layer closer to orrelative to another layer, such as a silicon semiconductor substrate,nor is there a reference with regard to removing an intermediate layerthrough the selective removal process.

The diffusion of one constituent toward the surface has been shown tocause preferential sputtering in alloys of Ni--Ag and Cu--Ni and incompounds PtSi, MoSi₂ and NiSi requiring corrections to depth-profilingmeasurements of the composition. See for example J. Fine, T. D.Andreadis and F. Davarya, Nucl. Instr. and Methods 209/210 (1983)521-530; M. Shikata and R. Shimizu, Surf. Sci., 97 L363 (1980); and Th.Wirth, V. Atzrodt and H. Lange, phys. stat. sol. (a) 82, 459 (1984). Inthese cases, diffusion during ion etching establishes compositiongradients up to several micrometers deep determined by temperature andpreferential sputtering yields. Bilateral Ni/Ni₃ C has also been shownto develop highly preferential sputtering. K. Morita, H. Ohno, M.Hayashibara and N. Itoh, Nucl. Instr. and Methods in Phys. Res. B2(1984) 596-600.

In general, there has been no teaching in the prior art of combining amethod of mobilizing one of the types of atoms in a compound layerrelative to the other and selectively removing atoms from the compoundlayer in order to eliminate an adjacent intermediate layer comprised ofthe same type of atoms as are being selectively removed from theadjacent layer, whereby the surface compound layer becomes positionedcloser to a base layer through the controlled elimination of theintermediate layer, while the structure of the compound layer remainsessentially unchanged.

SUMMARY OF THE INVENTION

The need for removing the epi-silicon layer subsequent to the formationof a titanium silicide or other compound intermediate surface layeradjacent thereto in order to vertically position said surface layeradjacent to a semiconductor substrate layer while maintaining thestructural integrity of the surface layer is satisfied in accordancewith the principles of the present invention by providing a method forcontrolled positioning of a surface compound layer comprising at leasttwo types of atoms, one type being common-type atoms which typecomprises an adjacent intermediate layer, which intermediate layer isadjacent to a base layer, and a second type of atoms. The steps of themethod comprise heating said layers to a temperature at which one ofsaid types of atoms in the compound surface layer is relatively moremobile than the other of said types of atoms in said layer; selectivelyremoving common-type atoms from said surface layer such that theselectively removed common-type atoms are replaced by common-type atomsfrom the intermediate layer by diffusion; and controlling the selectiveremoval of the common-type atoms from said surface layer to control therelative diffusion of atoms between said surface layer and saidintermediate layer and thereby achieve a reduction of thickness theintermediate layer.

The invention further provides a method for controlling the position ofa compound surface layer in a multilayer device comprising the steps ofcreating an intermediate layer directly adjacent to a base layer, saidintermediate layer comprising a single type of atom; depositing orgrowing a surface layer directly adjacent to said intermediate layer,said surface layer comprising compound molecules wherein one of theatoms in said molecules is the same type or common-type as the atomscomprising the intermediate layer; and selectively removing common-typeatoms from the compound surface layer and simultaneously heating saidlayers to a temperature which causes one type of atom in the compoundmolecules to be substantially more mobile than the other type of atom insaid molecules; wherein the intermediate layer is reduced and compoundsurface layer is positioned closer to the base layer while itsstructural integrity is substantially unchanged.

It is a principal object of the invention to provide a method for thereduction or elimination of an intermediate layer which improves theconditions for formation of at least one layer of a multilayer, butwhich ultimately hinders the overall conductance of the semiconductordevice.

It is also a principal object of the invention to improve a method forpositioning a contact compound layer adjacent to and in good contactwith the semiconductor substrate.

A principal advantage of the invention is that it provides a method offorming a multilayered semiconductor device with increased conductanceby removing an undesirable intermediate layer originally desired for theformation of an adjacent surface layer.

A further advantage of the invention is that it provides for thecontrolled positioning of a compound surface layer adjacent with a basesubstrate layer by removal of the intermediate layer originallyseparating the surface layer and the base layer.

A still further advantage of the invention is to provide for a sharper,cleaner contact between the compound surface layer and the semiconductorsubstrate base layer.

A still further advantage of the inventive method is the ability to usea comparatively thick layer of epi-silicon as an intermediate layer withwhich a compound silicide surface layer is formed thereon, therebymaking the formation of the compound layer easier and reducing thelikelihood of a reaction between the metal and the doped semiconductorbase layer.

A prime feature of the invention is the capability to remove theintermediate layer subsequent to the formation of the desired surfacelayer while maintaining the structural integrity of the newly formedsurface layer and the underlying semiconductor substrate base layer.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, aspects, features and advantages of the presentinvention will be more readily understood from the following detaileddescription when read in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a cross-sectional schematic view of a portion of a typicalCMOS multilayered device.

FIG. 2 is a cross-sectional schematic view of a portion of a CMOS deviceof the type shown in FIG. 1 subsequent to the formation of a C-49crystallized titanium silicide layer (TiSi₂).

FIG. 3 is a cross-sectional schematic view of a portion of a CMOS deviceof the type shown in FIG. 1 wherein the remaining epi-silicon layer (32)is comparatively thicker than in FIG. 2.

FIG. 4 is a cross-sectional schematic view of a portion of a typicalCMOS device of the type shown in FIG. 3 subsequent to the steps of theinventive method.

FIG. 5 is a schematic view of the effects on a CMOS device of the typeshown in FIG. 3 during Ar⁺ ion bombardment at a temperature of less than400° C. over time.

FIG. 6 is a schematic view of the effects on a CMOS device of the typeshown in FIG. 3 during Ar⁺ ion bombardment at a temperature of between500° and 700° C. over time.

FIG. 7 is a graph showing the relationship between the conductance of aCMOS device having a titanium silicide surface layer and time during Ar⁺ion bombardment at various temperatures.

FIG. 8 is a graph showing the Rutherford Backscattering Spectradisplaying the loss of titanium and silicon atoms during Ar⁺ ionbombardment for 15 minutes at various temperatures.

FIG. 9 shows the Rutherford Backscattering Spectra of a samplecontaining an implanted Xe marker showing that Si atoms move during anAr⁺ ion bombardment at 300 eV at 600° C.

FIG. 10 is a graph showing the relationship between the step heightmeasurements relative to adjacent masked areas during ion bombardmentand various temperatures.

FIG. 11 shows the sputtering yield of a CMOS device of the type shown inFIG. 3 in atoms per ion during an ion beam bombardment over atemperature range from 0° C. to 700° C.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

There will now be described a method for the controlled positioning of acompound layer in a multilayer device.

FIG. 1 shows an epi-silicon layer (12) sandwiched between a siliconsubstrate (11) and a titanium layer (13). An optional silicon dioxideinsulating layer (14) is abutting and adjacent to the multilayers (11,12, and 13).

FIG. 2 shows a C-49 crystallized titanium silicide layer (TiSi₂) (23)resulting from a typical annealing process wherein the titanium layer ofFIG. 1 (13) is reacted with a portion of the epi-silicon layer of FIG. 1(12). The unreacted titanium is selectively etched away using either anacid or base solution in the presence of an oxidizing agent as routinelydone by those skilled in the art. There remains the unreacted portion ofthe epi-silicon layer (22).

FIG. 3 has a comparatively thicker epi-silicon layer (32) than inFIG. 1. The surface layers of TiSi₂ (33) has undergone the standardanneal process to form a C-49 crystalline structure.

FIG. 4 shows the CMOS device subsequent to the steps of the inventivemethod performed thereon wherein the C-49 TiSi₂ layer (43) is positionedadjacent to the silicon substrate (41) and the intermediate epi-siliconlayer of FIG. 3 (32) has been fully consumed.

FIG. 5 shows a silicon substrate as a base layer (51), an epi-siliconintermediate layer (52), and a titanium silicide surface layer (53)during Ar⁺ ion bombardment selective sputtering of the surface layer(53) at a temperature of less than 400° C. over time. The figureillustrates that the surface layer (53) is consumed and the intermediatelayer (52) remains substantially intact.

FIG. 6 shows a silicon substrate base layer (61), an epi-siliconintermediate layer (62) and a titanium silicide surface layer (63)during the inventive process of ion bombardment selective sputtering ofthe surface layer (63) at a temperature of between 500° and 700° C. overtime. FIG. 6 illustrates that the intermediate layer (62) is consumedover time while the surface layer (63) remains substantially intact.

In selecting the proper configuration for the multilayer device uponwhich the inventive method is best practiced, it is preferred to have anembodiment wherein there are at least three (3) contiguous layers suchthat the middle or intermediate layer is required to be present duringthe formation or creation of at least one of the other two adjacentlayers, but wherein it is also desirable to eliminate or reduce theintermediate layer after such formation has occurred so that the layersimmediately adjacent to the intermediate layer are positioned in directcontact with each other. Referring now to FIGS. 1, 2, and 3, the primarysubstrate (11, 21, and 31) is hereinafter referred to as the base layer,the middle layer (12, 22, and 32) is the intermediate layer and thelayer adjacent to the remaining side of the intermediate layer isreferred to as the surface layer (13, 23, and 33). The process of movinglayers relative to each other is referred to as positioning and in thecase of a stacked layered embodiment, as vertical positioning,regardless of the device's orientation.

It is equally important to select the proper composition for each layer.The base layer may be any compound compatible with the adjacentintermediate layer and which is ultimately compatible with the surfacelayer. In a CMOS or other semiconductor device, such a base layer isfrequently a semiconductor substrate such as silicon and is frequentlydoped with N-type or P-type dopants for better conductivity.

The adjacent intermediate layer is comprising atoms which are desirableto be present throughout or during the formation of the surface layer.In particular, in semiconductor technology, it is frequently desirableto have a purely undoped or lightly doped silicon intermediate layercommonly known as epitaxial silicon or epi-silicon as the intermediatelayer. The epi-silicon layer has good reactive qualities with titaniumand other positive metals which react to form a silicide. For reasonsstated above, direct reaction of the positive metal of a compound with adoped silicon base layer is less desirable.

Although epi-silicon is the preferred embodiment comprising theintermediate layer, germanium may also be used along with othercompounds which react well with the positive atoms in the surfacecompound layer.

The surface layer is formed or grown by reaction with the intermediatelayer so as to be positioned directly adjacent to the intermediatelayer. The surface layer, once formed, is a compound layer having one ofthe types of atoms as is present or in common with the intermediatelayer. Selection of a good compound is achieved by using compounds witha diffusion differential greater than about 10:1. Such compounds whichqualify for good compound layer include, but are not limited to,titanium silicide (TiSi₂) or cobalt silicide (CoSi₂). Compounds madefrom Germanium would also be suitable. The formation of the surfacelayer is dependent on techniques used by those skilled in the art, suchas a standard annealing process.

Once the structure and configuration of the multilayer CMOS device areselected, the multilayer device is heated to a temperature above 400° C.and preferably between about 500° C. and 700° C. with a temperature ofabout 600° C. being the most optimal. Simultaneously, the compoundsurface of the multilayered device is preferentially etched bybombarding the surface layer with argon ions generated by a relativelylow ion energy source having a generation voltage of less than about1,000 eV and preferably about 300 eV. Ion bombardment is used to achievea selective scattering or sputtering from the top of the surface layerof those atoms which are in common with the intermediate layer referredto as common-type atoms.

Ion beams bombardment of the surface layer may be generated by a Kaufmanion source, a radio frequency plasma, a microwave (ECR) source, a plasmasource, or by other generators known by those skilled in the art. Argonions (Ar⁺) have been used as suitable ions for the bombardment but otherions may be used for bombardment methods, such as, Ne⁺, Kr⁺, Xe⁺. Inplace of ion bombardment scattering or sputtering methods, a chemicalselective removal means may also be used, such as a reactive etching orplasma etching process. Conceivably, any selective removal process whichcan accomplish the required removal of selected atoms from the surfacelayer at the required temperature range could be substituted.

The selection of the temperature range and the etching or sputteringprocedure is critical. In order to obtain a highly selective removal ofcommon-type atoms from the surface layer, the temperature should bebetween about 500° C. and 700° C. Schematic FIG. 5 illustrates thatwhere titanium silicide comprises the surface layer, temperatures ofless than 400° C. result in the depletion of the surface layer (53)instead of the intermediate layer 52. FIG. 7 shows that at roomtemperature (33° C.) the conductance of the device reaches zero withintwenty-five minutes of the commencement of the ion bombardment, whichindicates the surface layer is fully consumed. Schematic FIG. 6illustrates that where the Ar⁺ ion bombardment of the surface layer isconducted at a temperature of between about 500° and 700° C., theintermediate layer 62 is depleted and the surface layer 63 remainsintact and is thereafter positioned adjacent to the base layer 61thereby replacing the depleted intermediate layer 62.

EXAMPLE I

A titanium film of 100 nanometers is deposited on a layer of puresilicon (epi-silicon) which is situated adjacent to a doped siliconsemiconductor substrate. The titanium deposit is reacted with a portionof the adjacent epi-silicon layer by annealing the sample at 675° C. for30 minutes in nitrogen gas to form a 230 nanometer thick layer comprisedessentially of C-49 crystalline TiSi₂. A standard selective chemicaletch is conducted on the titanium silicide surface layer using an acidsolution of sulfuric acid and peroxide as an oxidizing agent to removethe excess unreacted titanium. The sample is heated to 600° C. and,simultaneously, subjected to Ar⁺ ion bombardment at 300 eV with a fluxof 0.2 mA/cm².

The mechanism believed responsible for the effectiveness of the presentinventive method is a combination of the highly selectively removal ofthe atoms from the surface compound layer which are common to both theintermediate layer and the compound surface layer and either the abilityof the remaining atoms in the surface layer to diffuse to and react withthe atoms in the intermediate layer to reform the compound or theability of the atoms in the intermediate layer to diffuse into thesurface layer to react with the remaining atoms in the surface layerand, thereby, replace the atoms which are selectively removed to reformthe compound molecules. The diffusion is accomplished by making the onetype of atom more mobile than the other atom in the compound molecules.

In the case of a surface layer of cobalt silicide (CoSi₂) and anintermediate layer of epi-silicon, it is believed that the priormechanism is operative, wherein the Co atoms are more mobile than the Siatoms and, thus, the Co atoms diffuse to react with the epi-siliconintermediate layer.

In the case of a titanium silicide (TiSi₂) surface layer and anepi-silicon intermediate layer, it is believed that the second mechanismcontrols wherein the Si atoms are more mobile than the Ti atoms andthus, the silicon atoms from the intermediate layer diffuse into thesurface layer.

It is believed that at room temperature, preferential or selectivesputtering alters the near surface composition of a compound tocompensate for the preferential sputtering, such that the netcomposition removed corresponds to the bulk composition. At hightemperatures, however, one species may be more mobile than the other. Ifthe more mobile species has a higher sputtering yield, then it iscontinuously removed from the surface of the surface layer while beingreplaced by the diffusion from the interior of the material.

The effectiveness of the inventive method over variations in temperatureis illustrated in FIG. 7 wherein the optimal normalized conductance(shown by a value of 1) occurs with an ion beam etching process at 600°C. At and below 400° C. the conductance drastically reduces over timeindicating that the surface layer of TiSi₂ is being etched away.

FIG. 8 shows the Rutherford Backscattering Spectra of a bombarded samplefor various temperatures. At 33° C. the titanium peak indicates that thetitanium in the surface layer is being removed by sputtering. At 700° C.the spectra show that no titanium is removed. The tungsten (W) readingin the Rutherford Backscattering Spectra is caused from somecontamination of the sample as a result of ion beams hitting thetungsten probes used to monitor sheet resistance during ion etching.FIG. 9 shows the Rutherford Backscattering Spectra for the sample inExample I above. In this sample, a Xe marker shows that the dominantmoving species is Si and not Ti.

FIG. 10 shows the step height of the ion bombarded surface relative toadjacent masked areas during ion bombardment at various temperatures(solid line). The surface of the silicide is recessed over 2000angstroms at temperatures above 500° C., while the RutherfordBackscattering spectra (FIG. 8) show that the thickness of the silicideremains substantially unchanged. The recess is believed to be due to thesputter removal of silicon which has diffused to the surface frombeneath the silicide. The dotted line in FIG. 10 shows the ratio of thediffusion distance of Si atoms in 1 second (d) to the thickness ofsilicide sputtered from the surface in 1 second (a) as a function oftemperature. The ratio d/a exceeds unity at about 500° C., indicatingthat at temperatures above 500° C., diffusion of Si is fast enough toreplenish the Si atoms removed from the surface by sputtering, therebyallowing the composition of the silicide to remain unchanged.

FIG. 11 shows the sputtering yield (number of atoms removed per incidentargon ion) during ion bombardment over a temperature range from 0° C. to700° C. The components of the sputtered atom flux are identified as Tiatoms from TiSi₂, Si atoms from TiSi₂, and Si atoms diffused frombeneath the TiSi₂ layer. At temperatures above 500° C., the sputteredatom flux is almost entirely composed of Si atoms diffused to thesurface from beneath the TiSi₂ layer.

Once a titanium silicide or cobalt silicide surface layer is positionedadjacent to a silicon substrate base layer because the intermediateepi-silicon layer is removed, the practitioner may desire to convert theC-49 titanium silicide surface structure to a C-54 titanium silicidestructure to obtain optimum low resistance in the CMOS device. Theconversion can be accomplished by a standard anneal used by thoseskilled in the art.

While the invention has been described in terms of the preferredembodiments, those skilled in the art will recognize that the specificconfigurations, steps and parameters may be varied in the practice ofthe invention by those skilled in the art without departing from thespirit of the invention, the scope of which is defined by the appendedclaims.

Having thus described our invention, what is claimed is:
 1. A method forcontrolled positioning in a semiconductor device of a surface compoundlayer comprising silicide having at least two types of atoms, one typebeing common-type atoms which type comprises an adjacent intermediatelayer, which intermediate layer is adjacent to a base layer, and asecond type of atoms comprising the steps of:heating said layers to atemperature at which one of said types of atoms in the compound surfacelayer is relatively more mobile than the other of said types of atoms insaid layer; selectively removing common-type atoms from said surfacelayer such that the selectively removed common-type atoms are replacedby common-type atoms from the intermediate layer by diffusion; andcontrolling the selective removal of the common-type atoms from saidsurface layer to control the relative diffusion of atoms between saidsurface layer and said intermediate layer, thereby reducing thethickness of the intermediate layer.
 2. A method according to clam 1wherein said intermediate layer is silicon or epitaxial silicon.
 3. Amethod according to claim 2 wherein said silicide is titanium silicideor cobalt silicide.
 4. A method according to claim 1 wherein saidheating step comprises heating said layers to a temperature of betweenabout 500° C. and 700° C.
 5. A method according to claim 2 wherein saidheating step comprises heating said layers to a temperature of betweenabout 500° C. and 700° C.
 6. A method according to claim 3 wherein saidheating step comprises heating said layers to a temperature of betweenabout 500° C. and 700° C.
 7. A method according to claim 4 wherein saidheating step comprises heating said layers to a temperature of about600° C.
 8. A method according to claim 5 wherein said heating stepcomprises heating said layers to a temperature of about 600° C.
 9. Amethod according to claim 6 wherein said heating step comprises heatingsaid layers to a temperature of about 600° C.
 10. A method according toclaim 1 wherein said selectively removing step comprises ion bombardmentpreferential etching or sputtering, or chemical ion etching or plasmaetching.
 11. A method according to claim 2 wherein said selectivelyremoving step comprises ion bombardment preferential etching orsputtering, or chemical ion etching or plasma etching.
 12. A methodaccording to claim 3 wherein said selectively removing step comprisesion bombardment preferential etching or sputtering, or chemical ionetching or plasma etching.
 13. A method for controlling the position ofa compound surface layer comprising silicide in a multilayersemiconductor device comprising the steps of:creating an intermediatelayer directly adjacent to a base layer, said intermediate layercomprising a single type of atom; depositing or growing a surface layerdirectly adjacent to said intermediate layer, said surface layercomprising compound molecules wherein one type of atoms in saidmolecules is the same type or common-type as the atoms comprising theintermediate layer; and selectively removing common-type atoms from thecompound surface layer and simultaneously heating said layers to atemperature which causes one type of atoms in the compound molecules tobe substantially more mobile than the other type of atoms in saidmolecules, wherein the thickness of the intermediate layer is reducedand the compound surface layer is positioned closer to the base layerwhile its structural integrity is substantially unchanged.
 14. A methodaccording to claim 13 wherein said intermediate layer is silicon orepitaxial silicon.
 15. A method according to claim 13 wherein saidsilicide is titanium silicide or cobalt silicide.
 16. A method accordingto claim 13 wherein said selectively removing step comprisespreferential ion beam etching, or sputtering, or chemical reactive ionetching or plasma etching.
 17. A method according to claim 14 whereinsaid selectively removing step comprises preferential ion beam etching,or sputtering, or chemical reactive ion etching or plasma etching.
 18. Amethod according to claim 15 wherein said selectively removing stepcomprises preferential ion beam etching, or sputtering, or chemicalreactive ion etching or plasma etching.
 19. A method according to claim13 wherein said heating step comprises heating said layers to atemperature of between about 500° C. and 700° C.
 20. A method accordingto claim 14 wherein said heating step comprises heating said layers to atemperature of between about 500° C. and 700° C.
 21. A method accordingto claim 15 wherein said heating step comprises heating said layers to atemperature of between about 500° C. and 700° C.
 22. A method accordingto claim 19 wherein said heating step comprising heating the layers to atemperature of about 600° C.
 23. A method according to claim 20 whereinsaid heating step comprising heating the layers to a temperature ofabout 600° C.
 24. A method according to claim 21 wherein such heatingstep comprises heating said layers to a temperature of about 600° C.